Automatic lubrication means for plural stage compressors



Aug. 12, 1952 H, B, PQWNALL, 2,606,430

v AUTOMATIC LUBRICATION MEANS FOR PLURAL STAGE coMPREssoRs Filed Aug. 24, 1951 4 sheets-sheet 1 INVENTOR Hnryl Powwai/ ATTORNEY IN. @mi

H. B. POWNALL.

AUTOMATIC LUBRICATION MEANS FR PLURAI.. STAGE COMPRESSORS Filed Aug. 24, 1951 Aug.1z, 1952 4 Sheets-Sheet 2 INVENTOR IYenryl?. Pou/wai?) Y hD ATTORNEY Aug. 12, 1952 H. B. PowNALL AUTOMATIC LUBRICATION MEANS FOR PLURAL. STAGE COMPRESSORS Filed Aug. 24, 1951 4 Sheets-Sheet 3 INVENTOR Hmzg PowmzZ/'Z/ y .mmmlhNl ATTORNEY Aug- 12, 1952 H. B. PowNALL AUTOMATIC LUBRICATION MEANS FOR PLURAI.. STAGE COMPRESSORS Filed Aug. 24, 1951 4 Sheets-Sheet 4 Patented Aug. 12, 1952 AUTOMATIC LUBRI'CATION MEANS FR PLURAL STAGE COMPRESSORS HenryaPoWnalI, York, Pa., assigner to Freezing Equipment Sales, Inc., York, Pa., a corporation of Pennsylvania Application August 24., 1951, Serial No. 243,530

This invention relates to lubricating systems and more particularly to lubricating systems for compressors ofthe plural stage type. Perhaps the principal use of this invention will be in connection with plural stage refrigeration systems and the invention will be described herein with particularreference to refrigeration systems, although it is believed that the same principles will be equally applicable in many cases to plural stage compression systems in general.

In the refrigeration art there has been a marked increase in the demand for extremely low temperature rooms and warehouses. rThis has been occasioned. in part at least,`by the demand for increased storage facilities for frozen food products as well as for refrigerate space for testing machinery of all kinds.

It has been found that rotary type compressors can be used to good advantage in plural stage refrigerationusystems, andparticularly in the low or intermediate stages of suchv systems, However, the problem of satisfactory and reliable lubrication for the low and intermediate stage machines has proven troublesome. These troubles are inherent in the use of suchdevices as Mansell lbricators. The chief difficulty in using lubricators of this type is that they require constant attendance in order to insure that there is, atall tihies, adequate supply of lubricant furnished to the rotary machinej and, further to insure that the oil level in the crankcas'e of the piston machine or niahifis, doesr Vnotrise Vabove the opr'ating level. y

It is an object of this ini/enti'on to provide a fully' automatic lubricating means for plural stage refrigeration syste''is which will substantially eliminate the need for manual attendance.

Other objectsf this invention will be apparent from the following description read in conjunction with theV attached drawings, in which:

1 Figure 1 shows a two stage system in which the high stage compressor is of the piston type'and the low stage machine is of the rotary type.

Figure 2 shows a three stage system in which the high stage machine is of the piston type and the intermediate and low stage machines are of the rotary type.

Figure'S shows a three stage' system in which the intermediate andhigh stage' machines are of the piston type and the low stage machine is of the rotary type.

Figuresv shows Ya two stage system in which piston type machines are used for both stages.

Y In each of the figures, corresponding parts have been given the same reference numerals.

In order' that the lubricating means of this invention may be workable in refrigerationsystems it must be used with a refrigerant in which theroil is mis'cible. All refrigerants of the Freon group satisfy this requirement while ammonia foreirample, does not. i

The oil which is pumped by a piston type com- 13 claims. (c1. -117.6)

2 presser in a single stage refrigeration system, eventually reaches equilibrium with Jthe oil which is returned from the evaporator to the intake of the compressor. In a plural stage refrigeration system such as shown in Figure l, however, regardless of how oil is fed to thebearings of the rotary machine, so lon:T as an ample supply is fed, there will be an overflow into the compressor proper which will go out the discharge side of the low stage machine, and be fed from there directly to the suction side of the high stage inachine. Under these conditions, the amount of oil returned to theusuction side of the high stage machine will always be in excessuofV the normal pumping rate of the piston machine and this will inevitably result inua raising level `of oil in the crankcase of the latter machine.

In general the disclosure of Figure i, ,solves the lubrication problem as follows:

An oil separator is conrected to the discharge line of the high stage machine and the oil output from this separator is fed to an oil receiver.

The oil in the latter is placed under a pressure which is positive with respect to the pressure on the discharge sideof the low stage machine. An outlet line connects" the Yoil receiver with the end bearings of the rotary machine through a pair of oil metering valves. In addition, there is provided a connection between the crankcase of the high stage machine and the suction or inlet side of the low stage machine.

Referring still to Figure l of the attached drawings for a more complete understanding of the instant invention, there is shown a two stage system which illustrates the invention in a simple form. rihe basic refrigerant circuit shown includes a low stage rotary machine i5, a high stage piston machine ii, a condenser i2 and an'evaporator i3. Interposed in line itl, which connects the discharge side of the high stage machine to the condenser, is an oil separator E5, and the usual thermal expansion valve l is interposed in line il between the condenser and the evaporator. Valve i3 may conveniently be of the superheat type controlled by the bulb I8. As will be apparent to those skilled in the art, refrigerant which has boiled off as gas in the evaporator is withdrawn through line i9 to the suction inlet of the low stage rotary compressor lil. The rotary machine compresses the refrigerant and feeds it through line 25 to the suction inlet of the high stage machine, and the latter delivers refrigerant, largely in liquid form, through line i4 to the condenser l2 by way of the oil separator l5. Liquid refrigerant from the condenser i2 under control of the thermal Valve it is then readinitted to the evaporator i3 and this completes the basic refrigerant circuit.

The oill separator i5, of conventional construction, is effective to separate about ninety percent of the oil contained inthe discharge from the high stage machine. This oil is fed through a 3 line 22 to an oil receiver 23. The oil in the receiver must be maintained at a pressure which is positive with respect to the discharge pressure of the low stage machine. This is accomplished, as shown in Figure l, by means of a small oriced bleed line 24 connected between the discharge from the high stage machine in line I4 to line 22. Unless this pressure is maintained at the proper level, the system will not work. Accordingly a pressure differential valve 25 is connected between the oil receiver and the discharge side of the rotary compressor. This valve as shown is paralleled by a pressure diierential switch 26, which conveniently may be arranged to shut down the entire system, in the event that the proper pressure is not maintained in the oil receiver. From the oil receiver, oil is fed through line 21 to a manifold 28 and from there a pair of lines 29 and 30 carry the oil, under pressure, to the end bearings of the rotary machine through oil metering valves 3 l and 32.

With the system as thus far described, oil under pressure will be fed continuously to the end bearings of the rotary machine, and in such quantity that it will overflow into the compressor chamber where, being miscible with the refrigerant it will be carried out the discharge of the rotary machine and returned to the suction inlet of the piston machine. As stated above, under these conditions oil is returned to the piston machine at a somewhat higher rate than the normal pumping rate of the piston machine. Consequently the oil level in the crankcase has a tendency to rise to a higher level than is desired. In order to stabilize the crankcase oil level and render the system fully automatic, a line 33 is connected between the crankcase of the piston machine and the suction inlet of the rotary machine, through an oil metering valve 34 of the same type as valves 3l and 32. The point of connection of line 33 to the crankcase of the piston machine is at the normal crankcase oil level, and any time, therefore, that the oil level rises above this point, the pressure dilerential existing between the crankcase of the piston machine and the suction inlet of the rotary machine will cause oil to be forced through line 33 to the suction inlet of the rotary machine. Here it will be mixed with refrigerant and returned to the inlet of the piston machine. In this way, equilibrium conditions are established insofar as oil level in the crankcase of the high stage machine is concerned, and adequate lubrication of the rotary compressor bearings is maintained.

It will be apparent to those skilled in the art that the oil metering valves 3|, 32 and 34 serve to restrict the flow of oil and to maintain a pressure differential in the conduits in which they are connected.

The above described automatic lubrication system is equally applicable to refrigeration systems employing more than two stages. Further examples illustrating the application of the broad principle of the present invention to three stage systems are shown in Figures 2 and 3.

In Figure 2, a second rotary machine 37 has been added to provide a third or intermediate stage, While in Figure 3, a piston machine 33 has been added to provide a third or intermediate stage. In each case, the same general lubrication scheme is used. In Figure 2 the suction inlet of the low stage machine IU as well as the end bearing members are lubricated directly from the oil receiver through lines 2l, 29, 30 and 39, manifold 28 and oil metering valves 3|, 32 and 34. The

intermediate stage rotarym'achinehas its end bearings lubricated directly from the oil receiver through an extension 40 of line 21, a second manifold 4|, lines 42 and 43 and metering valves 44 and 45. The crank-case oil level of the high stage machine is stabilized, as in Figure 1, by a conduit 33 connecting the crankcase of the piston machine l I to the suction inlet of the intermediate stage rotary machine 3l, through an oil metering valve 34A. Otherwise the system is the same.

In Figure 3 the crankcase level in the intermediate stage piston type machine is stabilized, as in Figures 1 and 2, by a connection 3l to the suction inlet of the low stage rotary machine. The crankcase oil level in the high stage machine is stabilized by a line 35 connected between' the crankcase at the normal -oil level to the oil receiver, through a throttling valve 33. This same line 35 in the system shown in Figure 3, takes the place of orificed bleed line 24 of Figure 1 and serves as a source of pressure for the oil receiver which is above the discharge pressure of the low stage machine.

Referring now to Figure 4 of the attached drawings, a two stage refrigeration system is shown. This system makes use of piston type compressors for both the low and high stages. The low stage piston machine 41 is connected similarly to the low stage rotary machine l0,

shown in Figure 1, and since the refrigerant circuit is identical, no further discussion is believed necessary. The oil separator l5 is connected, as before, between the discharge from the high stage machine and the input to the condenser with the oil line 22 connecting the oil separator to the oil receiver 23. The output line 27 from the oil `receiver in this case, however, leads to the suction inlet of the low stage machine rather than to a manifold or distributing header as shown in the other gures of the drawings. A line 48 is connected intermediate the crankcase of the high stage compressor at a point substantially corresponding to the normal oil level therein and the top of the oil receiver 23, in order to stabilize the oil level in the high stage compressor. A pressure differential valve 25 is connected in the same way as in the apparatus shown in Figure 1, i. e., between the top of the oil receiver and the discharge side of the low stage machine. This valve serves, as before, to maintain a substantially xed pressure differential between the oil receiver and the discharge side of the low stage compressor.

It will be apparent to those skilled in the art that this invention is not limited in its application to the specific two and three stage systems shown in the accompanying drawings but in fact has wide application in plural stage refrigeration and compression systems. It will also be apparent that by means of this invention a fully automatic lubricating system for plural stage refrigeration apparatus has been provided.

I claim:

l. A two stage refrigeration system in which a piston type compressor is used for the high stage and a rotary type compressor is used for the low stage, and in which the rotary compressor discharges lrefrigerant into the suction inlet of the piston compressor: means for furnishing an ample supply of oil to the end bearings of the rotary compressor; a closed lubricant conduit connected between the crankcase of the high stage compressor at a point corresponding substantially to a normal oil level therein, 'and the suction inlet acca/iso intermediate stages, and in which the low stagey compressor'discharges refrigerant into the suc'- tion' inlet of the interemiate stage compressor and the latter discharges refrigerant into the suction inlet ofthe high stage compressor: vmeans for furnishing an alpl Supply of Oil `ttl th end bearings `of the rotary compressors and t the suction inlet of the low stage rotary compressor;

a closed lubricant conduit connected between the "whereby the oil level in the cranlcase ofthe vhigh stage machine 'is stabilized and lubricant is .sup-

plied to the rotary compressors duringoperation lofthe system.

`s: A threestage registration systemiswhich a rotary compressor is used for the low stage vand piston type' compressors are used for the highr and intermediate stages, and in which the low stage compressor discharges refrigerant into the suction inlet of the intermediate stage compressor Vand the latterV dischargesrefrigerant into the suction inlet of the high stage compressor: means including an'oil separator connected in thedis.- charge line of the high stage machine and an oil receiverv for furnishing an ample amount of` oil to the end bearings of the vrotary compressor; a

closed lubricant conduit connected between the crankcase of the intermediate stage compressor at a point corresponding to a normal oil level therein and the suction inlet of the low stage rotary `compressor in order to stabilize the oil level in the crankcase of the intermediate stage compressor; means operatively connected in said cony duit for restricting Vthe-flow therein and for maintaining a pressure differential in said conduit between said compressors; a second closed lubricant conduit connected between the crankcase of the high stage compressor at a point corresponding maintaining a pressure differential in said conduit between said compressors; whereby the oil level in the high stage compressor is stabilized and oil is supplied to the lower stage compressors during operation of the system.

4. In a plural stage refrigeration system in which at least one compressor is of the rotary and one of the piston type, the latter being the high stage machine, an automatic lubricating means comprising: an oil separator connected to the high pressure side of the piston type compressor to eiect separation of oil from refrigerant; an oil receiver connected to the oil discharge side of said oil separator; means for maintaining the oil in said receiver under apressure which is positive with respect to the rotary compressor discharge pressure; closed lubricant conduits connecting said 'oil receiver and rotary compressor 'for lubricating said rotary compressor; means operatively connected in each of said conduits for restrictingv the flow therein and for maintaining a pressure diierential in said conduits; a lubricant bleed line connected between the crankcase of the piston compressor and the suction inlet of the rotary compressor, said line having a; flow restricting valve operatively connected therein for preventing oil in the crankcase of the piston compresser from rising above a predetermined level.

5. A plural stage refrigeration system comprising: at least two compressors, the discharge of one being connected to the suction inlet of the other, and at least' one of which is of the piston and oneof the rotary type, the piston compressor being the high stage machine; an evaporator; a condenser; closed-refrigerant carrying conduits connecting said compressors, condenser, and evaporator in a normal refrigeration circuit; means for furnishing lubricant to the end bearings of said rotary compressor; closed lubricant conduit means connected between the crankcase of said piston compressor and the suction side of a rotary compressor operating in the system as a lower lstage compressor; and means operatively connected in said conduit for restricting the now and lmaintaining a pressure differential therein.

6. A plural stage refrigeration system comprising: a piston type high stage compressor; a rotary type low stage compressor; a condenser; an evaporator; closed fluid conduits connecting said compressors, condenser, and evaporator, in a closed normal refrigerant circuit; an oil separator interposedy between the discharge of the high stage machine and the inlet of the condenser; an oil receiver connected to the oil outlet of said oil separator; an oriced lubricant bleed line connected between the discharge side of said piston type compressor and said oil receiver; closed lubricant conduits connecting said oil receiver to the end bearings of said rotary compressor; meansoperatively connected in said conduits for restricting the ilow and maintaining a pressureY stage compressor at a predetermined level.

7. A plural' stage refrigeration system comprising: a piston type high stage compressor; a rotary type low stage compressor; a rotary type intermediate stage compressor; a condenser; an evaporator; closed fluid conduits connecting said compressors, condenser, and evaporator, in a closed normal refrigeration circuit; an oil separator connected between the discharge of said high stage compressor and the inlet of said condenser; an oil receiver; a closed lubricant conduit connect- =`ing the oil discharge side of said oil separator Y and said oil receiver; an oriced lubricant bleed rotary compressor; means operatively connected in each of said conduits for restricting the flow and maintaining a pressure differential therein; and a closed lubricant conduit connecting the crankcase of said high stage compressor to the suction inlet of said intermediate stage compressor, said conduit havingmeans operatively connected therein for restricting the flow and maintaining a pressure diierential to maintain a predetermined oil level in the crankcase of said high stage compressor.

8. A plural stage refrigeration system comprising: a low stage rotary compressor; an intermediate stage piston type compressor; a high stage piston type compressor; a condenser; an evaporator; means including closed iiuid conduits connecting saidcompressors, condenser and evaporator in a closed normal refrigeration circuit; an oil separator connected to the discharge side of said high stage compressoryan oil receiver; closed lubricant conduit means connecting the oil discharge side of said oil separator to said oil receiver; a pressure differential valve connected between said oil receiver and the suction inlet side of said intermediate stage piston compressor; closed lubricant conduits connecting said oil receiver to the end bearings of said low stage rotary compressor; means operatively connected in each of said closed conduits for restricting flow and maintaining a pressure differential therein; a closed lubricant conduit connecting the crankcase of said intermediate stage compressor to the suction inlet of said low stage rotary compressor; means operatively connected in said conduit for restricting the flow and maintaining a pressure differential therein; and means including a closed lubricant conduit connecting the crankcase of said high stage compressor to said oil receiver, said conduit having a'flow restricting valve therein; whereby a predetermined oil level is maintained in the crankcase of said piston type compressors.r

9. A plural stage refrigeration system comprising: a low stage piston type compressor; a high stage piston type compressor; a condenser; an evaporator; means including closed fluid conduits connecting said compressors, condenserand evaporator in a closed normal refrigeration circuit; an oil separator connected to the discharge side of said high stage compressor; an oil receiver; closed lubricant conduit means connecting the oil discharge side of said oil separator to pressor; and means including a closed lubricant conduit having a flow restricting valvetherein connecting the crankcase of said high stage compressor to said oil receiver, whereby a predetermined oil level is maintained in the crankcase of said high stage compressor.

10. Lubricating means for a plural stage refrigeration system of the type in which a low stage compressor discharges refrigerant into the suction inlet of a high stage compressor and in which a piston type compressor is used for the high stage, the said means comprising: a closed lubricant conduit connected intermediate the crankcase of the high stage compressor at a point corresponding substantially to a predetermined oil level therein and the suction inlet of a lower stage compressor; and means operatively connected in said conduit for restricting the flow therein to maintain a pressure differential in said conduit Hrotaryrnach'ine; a' closed lubricant conduit connected intermediate the crankcase of the high stage machine at a point corresponding substantially to a normal oil level therein and the suction inlet ofthe rotary'm'achine; and means operatively connectedin said conduit for restricting thel flow therein to maintain a pressure differential in said conduit between said machines; whereby theoil level inthe crankcase of the high vstage machineA is stabilized and lubricant is supplied to the'V low stage rotary machine during operation of the system. l l

12. vLubricating means for a plural stage compression system of thetype in which a low stage compressor discharges refrigerant into the suction'inlet of `a high stage compressor and in which a pistonk type lcompressor is used for the high sta-ge, said means comprising; a closed lubricant conduit connected intermediate the crankcase of the high stage compressor at a point corresponding' substantially to a predeterminedY oil level therein and the suction inlet of a lower stage compressor; and means operatively connected in said conduit for restrictingthe flow therein to maintain a pressure rdiiferential in said conduit between said compressors; whereby the oil level in the crankcaseof the high stage compressor is stabilized and lubricant is supplied to said lower stage compressor during operation of the system.

'operates at asubstantially higher pressure than another compressor, and in which a lower stage compressor discharges'refrigerant into the suction inlet of the high stage compressor; condensing means; evaporating means; means connecting said compressors, condenser and evaporator 'means in a closed normal multi-stage refrigeration system; a closed lubricant conduit connected between the crankcase of the piston compressor at a pointvcorresponding substantially to a predetermined loil level therein and the refrigerant -suction inlet of a lower stage compressor; means operatively connected in said conduit for restrictingvthe ow therein and for maintaining a pressure diiferential in said conduit between said compressors; whereby the oil level in the crankcase of the high stage -piston compressor is stabilized and lubricant is'supplied to the lower stage compressor during operation of the system.

HENRY B. POWNALL.

' REFERENCES CITED The following references are of record in the file of thispatent:

UNITED STATES PATENTS `Name Date 2,140,415 Buehler, Jr. Dec. 13, 1938 y2,178,100 Gygax Oct. 31, 1939 Morrison Apr. 12, 1949 

